Worldwide concerns of resource scarcity and climate change are driving the search for carbon-neutral, renewable energy alternatives for fossil fuels. Organic wastes such as food waste represent an abundant domestic resource for energy production. Recognizing the potential embedded in organic waste, various energy conversion technologies have been developed. Food waste from the Colorado Convention Center in Denver, Colorado can be used as the substrate for a microbial fuel cell (MFC) reactor, a newly developed technology that directly converts waste to energy. Microbial fuel cells (MFCs) are bio-electrochemical reactors that use microbes as biocatalysts and convert biodegradable resources into electricity. Previous lab-scale experiments using Colorado Convention Center food waste showed a sustainable power density of 155 mW/m2 with a waste reduction of approximately 70%. Based on the encouraging preliminary data, a scaled-up version of a MFC reactor was designed and constructed as a continuous flow-through system using an air cathode.
The most cost-effective materials were used to manufacture this reactor including activated carbon cloth and stainless steel current collector to test the feasibility of scaling up a MFC reactor. A new coating, polydimethylsiloxane (PDMS), was also used to construct the scale-up MFC as a tubular reactor so that the cathode would have more efficient oxygen reduction capabilities. In addition, a fermentation chamber served as a holding tank for the scale-up MFC to assist with hydrolysis, which also helped to compare a MFC with a closed biodegradation system like anaerobic digestion.
Several parameters including chemical oxygen demand (COD) loading and hydraulic retention time (HRT) were optimized to achieve the best performance. The scale-up MFC was discovered to also have a waste reduction of approximately 70%, with the highest COD removal reaching about 90% and a power density around 19 mW/m2 or 1,865 mW/m3. A life cycle assessment (LCA) was also conducted to compare the energy input of manufacturing the scale-up MFC with the fossil fuels displaced from its electricity generation. This was also compared to food waste sent to a landfill and composting. These results will be used to help determine the feasibility of an on-site pilot scale MFC reactor for the Colorado Convention Center.